1. Field of the Invention
This invention concerns a novel oil-soluble molybdenum compositions useful as a lubricant additive.
Particularly, this invention concerns a lubricant composition containing an oil-soluble molybdenum compound which is excellent in anti-oxidation effect, anti-wear effect, friction reducing effect and mineral oil solubility, as well as excellent in view of metal corrosion, particularly, for copper, iron, etc.
2. Description of the Prior Art
Various kinds of compositions have been known so far as lubricant additive for use in engine oils and the like, but the performance demanded for the lubricant additives has become more severe in recent years in view of the resource saving and energy saving. For the improvement in the wear resistance, zinc dithiophosphate (hereinafter referred as ZDTP) has heretofore been used generally and, in addition, molybdenum dithiophosphate (hereinafter referred to as Mo-DTP) has also been used as disclosed in Japanese Patent Publications Nos. 8426/1965 and 27366/1969 or Japanese Patent Laid-Open No. 110796/1981, etc.
However, both of ZDTP and Mo-DTP contain phosphorus atoms and, since the total amount of phosphorus that can be added is restricted, taking into consideration the phosphorus poisoning of automobile exhaust gas purifying catalysts that are used. As one of the countermeasures for the atmospheric pollution, there is a certain limit on the amounts of compounds tht can be used.
While on the other hand, a number of molybdenum dithiocarbamate compounds (hereinafter referred to as Mo-DTC) have also been reported (refer to Japanese Patent Publications Nos. 6362/1974, 964/1976, 31646/1978, 12638/1981, etc.). However, although these compounds are free from the problems in view of the catalyst poisoning, they involve a serious drawback that the lubricating performance is not satisfactory and the solubility of them in the base oils such as mineral oils is poor.
In addition, these known ZDTP, Mo-DTP and Mo-DTC compounds have various drawbacks respectively as described above and it is particularly mentioned that they have a common major drawback namely a significant corrosive nature to metals (refer to SAE Paper 851260).
It has been considered essential that organic molybdenum compounds useful as lubricant additives should contain sulfur atoms in the molecules of the compounds. That is, has been considered that the lubricating performance can be obtained by the formation of molybdenum disulfide on the lubricating surface by molybdenum and sulfur contained in the molecules. However, the present inventors have assumed that active sulfur atoms contained in the molecules may have undesirable effects in view of the metal corrosion and have made an earnest study in order to overcome the contraction. As a result, it has surprisingly been found that although the product obtained by the reaction between a molybdenum compound and an amino compound has no substantial performance when used alone as a lubricant additive, it exhibits extremely satisfactory lubricating performance when combined with a sulfur-containing compound.